Description of REMUR

Description of the spectrometr of polarized neutrons given in works [1-3]. The REMUR reflectometer is designed to study properties of thin films, interfaces in multilayer structures, various types of ordering, self-organization in biological systems, etc. by the method of specular and off-specular neutron reflection from the surface of films. A polarized neutron beam is formed by a neutron-optical system consisting of a set of mirrors and diaphragms that specify necessary collimation and polarization of the beam. In the reflectometer the so-called slit geometry is used, in which a narrow neutron beam 0.1-1 mm wide is collimated by slits in the vertical direction. Neutron scattering occurs in the horizontal plane. Highly efficient adiabatic radio-frequency flippers [4] are used to reverse the neutron spin direction in a wide range of neutron wavelengths (0.9-10 Å). The analysis of polarization of the reflected beam is performed using wide-aperture fan mirror analyzer [5, 6]. The reflected beam is detected by two-coordinate gas 3He detectors with spatial resolution of about 2.5 mm.

Sample environment

Three-circle goniometer with an electromagnet mounted on top of it and generating external magnetic field in the range 0-20 kOe and making it possible to change the field direction with respect to the sample plane in the range of ± 90°.

There is a set of removable poles with cross sections: 40 × 20 mm2, 110 × 70 mm2 and 60 × 40 mm2.

The maximum magnetic field with a pole gap of 15 mm is 20 kOe for small poles with cross section of 40 × 20 mm2 and 10 kOe for large poles of 110 × 70 mm2.

Cryostat with a vertical magnetic field of up to 3 Tesla and T=1.45-600 K. The maximum sample size is 40x40 mm2.

Detectors

2D PSD

Gas mixture

3Не (2 atm) + CF4 (1.2 atm)

Working area

23 × 23 mm2

Spatial resolution (FWHM)

2.3 mm along the X axis and 2.7 mm along the Y axis

Characteristics of polarizers and polarization analyzer

Reflectometry polarizers PR1 and PR2

Substrate sizes

28 × 100 × 800 mm3

Polarized beam cross section

0.24 ÷ 0.8 mm

Beam glancing angle

1 ÷ 3.3 mrad

Critical wavelength

0.86 ÷ 2.84 Å

Reflectometry fan analyzer

Number of mirrors

94

Substrate sizes

250 × 60 × 0.3 mm3

Channel cross section

– at the entrance

1.0 × 40 mm2

– at the exit

0.93 × 40 mm2

Beam capture angle in horizontal plane

27.3 mrad

Focal distance:

4400 mm

Flow area (vertical × horizontal)

40 × 120 mm2

“Geometrical” transmission

0.66

Coating on both sides

FeCoV/TiZr

Critical wavelength

1.3 Å

Fan polarization analyzer

The analyzer mirrors are arranged in the form of a fan with a focus on a sample at a distance of 4.45 m (Fig. 1). The neutron beam is reflected from a sample and comes to the analyzer. In this configuration the angle a between the scattered neutron beam and the analyzer mirrors remains constant for all beams reflected from the sample and the polarization efficiency of the analyzer does not depend on the angle of neutron scattering by the sample.

Adiabatic radiofrequency spin-flippers

Spin-flippers comprise two pairs of constant magnetic field coils and a radiofrequency coil with an alternating magnetic field frequency of 76 kHz. The amplitudes of constant and alternating magnetic fields of the spin-flipper show a sine-cosine dependence in the range of 10-40 Oe. To calculate the parameters of spin-flippers, the imposed requirement is that the neutron spin-flip probability be f(λ = 1 Å) ≥ 0.99. The experimental value of the neutron spin-flip probability f (λ) for a neutron wavelength interval of 1.4-10 Å is equal to unity within the limits of statistical errors. The length of spin-flippers along the beam is 800 mm, the neutron beam cross section is 150 mm.